Process of making antiknock motor fuels



March 20, 1934. v. VOORHEES 1,951,780

PROCESS OF MAKING ANTIKNOCK MOTOR FUELS Filed May 12, 1932 2 Sheets-Sheet l.

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PROCESS OF MAKING ANTIKNOCK MOTOR FUELS Filed May 12 1932 2 Sheets-Sheet 2 Stripper Fraction/E e INVENTOR MM 6m 30mm MM 9 characteristics.

Patented Mar. 20, 1934 1,951,780 PATENT OFFICE PROCESS OF MAKING ANTIKNOCK MOTOR FUELS Vandervcer Voorhees, Hammond, Ind., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application May 12, 1932, Serial No. 610,789

Claims.

This invention relates to the process of making motor fuels with a high knock rating, and particularly concerns a method of separating motor fuels into fractions of high and low knocking One object of the invention is to separate a motor fuel having intermediate knocking characteristics into a fraction having a high knock rating and a fraction having a low knock rating without chemically changing or destroying any of the original fuel. Another object of the invention is to produce a heavy naphtha gasoline fraction with a high knock rating suitable for blending purposes.

The knocking characteristics of a gasoline are conveniently designated by its octane number equivalent which is expressed as the percentage of iso-octane, in a mixture of iso-octane and normal heptane having the same knocking characteristics as the fuel in question, when employed in aninternal combustion engine. In general, straight-run gasolines made by direct distillation of crude petroleum possess low knock ratings and are unsuitable for use in modern gasoline engines with compression ratios of the order of 5.5 to 1, designed to operate on fuels having knock ratings of 60 to 80 or higher. Straight-run gasolines made directly from crude petroleum usually have knock ratings below octane equivalent depending on the type of crude oil from which they are made. Those-from naphthenie crudes have much higher knock ratings than those from parafiin base crudes. By the process herein described it is possible to start with a fuel having an octane number of 50 to 70 and separate therefrom a fuel having a knock rating satisfactory for high compression engines and a naphtha fraction unsuitable for internal combustion engine fuel but useful for a variety of other purposes. For carrying out the process, it is preferred to operate with a gasoline from a naphthenic or mixed base crude or a synthetic gasoline from a cracking process rather than a gasoline from a paraffin base crude.

The present process involves as the chief principle of operation the extreme refrigeration of the gasoline to a very low temperature whereupon the constituents responsible for the undesirable knocking characteristics will separate by crystallization. I have observed that the undesirable knocking properties of low antnknock gasolines fla are chiefly traceable to certain hydrocarbons of their detonation characteristics. When a gasoline containing normal parallin type hydrocarlions is subjected to severe refrigeration, either alone or with a suitable diluent, these constituents are found to selectively crystallize whereupon they can be removed from the mixture. -The separation of the undesirable constituents from gasolines of low knock rating can be accomplished in several ways such as chilling of the gasoline to a low temperature by means of cooling coils or direct refrigeration in contact with suitable liquefied refrigerating gases such as carbon dioxide, ammonia, propane, propylene, ethane, etc. and the hydrocarbons which crystallize may be removed by filtration, settling, centrifuging, or other suitable means adapted to low temperature operation. As an example of one modification of the process and by way of illustration I have appended. the accompanying, drawings Fig. 1 a partially diagrammatic layout of an apparatus for conducting the process and a second modification is illustrated in Fig. 2. The invention may be more fully understood by reference thereto.

The gasoline undergoing treatment, which may suitably be a distillate obtained directly from crude petroleum or a product of a liquid phase or vapor phase cracking process usually distilling within the gasoline boiling range between 80 and 450 F. is introduced by line 1 into fractionating column 2 where it is subjected to fractionation into a variety of relatively narrow boiling fractions. The heat for the fractionating operation may be supplied by a reboiler coil 3 and a suitable reflux-coil 4-. The-'drawing-s'illustrate asepara tion of the gasoline into five fractions, although this is merely by way of illustration, and fractions of any desired number and boiling range may be produced. For example, the light naphtha fraction may be removed as a single fraction and the heavy naphtha fraction may be divided into numerous narrow boiling fractions forfurther treatment.

Those fractions which are trapped out of the intermediate portion of the column may be stripped in suitable side strippers 5 and cooled in f coolers 6. The lightest fraction may be removed from the top of the column by line 7, condensed in condenser 8 and collected in receiver 9 whence it may be withdrawn by pipe 9a for processing or discharged from the system by pipe 96. The heaviest fraction may be withdrawn by line 10, cooled in coolers 11 and 12 and introduced into chiller 13.

For the purpose of this description it will be sufficient to describe in detail the operation of only one chiller. There are preferably provided as many chillers as there are fractions which it is desired to treat, although it is obvious that the process can be conducted inbatch cycles, treating only one fraction at a time, necessitating only one chiller. A variety of chilling devices may be employed, such as countercurrent heat exchangers, flash chambers, etc. For the purpose of this illustration I have described a process employing settling chambers into which the oil which is being treated is introduced and where it is allowed to settle during and subsequent to the chilling operation.

Referring again to the drawings, the heavy gasoline fraction which is introduced into chiller 13 is cooled by chilling coil 14 and maintained at a temperature suificiently low for the crystallization of the undesirable hydrocarbons which it contains. These hydrocarbons are waxlike in nature at the temperatures employed and precipitate to the bottom of the chiller where they are removed continuously by line 15. Sufiicient uncrystallized hydrocarbons may be allowed to accompany the waxy material to cause it to flow through the lines provided for removal and handling. However, it is generally desirable to make a more complete separation of the solid and liquid hydrocarbons and remove the solid material by suitable mechanical means such as a screw conveyor. The waxy material introduced into line 15 is conducted to heat exchanger 16 and thence to storage as indicated. The liquid hydrocarbons collecting in the top of chiller 13 are withdrawn continuously through line 17 and likewise pass through a heat exchanger 12 to storage. This operation is repeated in the remaining chillers and settlers, 18, 19, 20 and 21.

In the case of settlers 18, 19, 20 and 21, it may likewise be convenient to employ the cooling effect of the separated liquid hydrocarbons in reducing the temperature of the naphtha charged to the chiller as illustrated. Thus the liquid hydrocarbons separated in chiller 18 are passed by line 22 to heat exchanger 22a and thence by line 23 to storage. Various other means may be employed to conserve refrigeration but for simplicity I have shown the mixing of the solid fractions from each chiller in line 15 and the utilization of the refrigerating effect of this material by means of exchanger 16 where it assists in cooling and condensing the refrigerant gas.

The refrigerant employed may suitably be carbon dioxide by the use of which it is possible to reduce the temperature to l12 F. at which temperature it becomes a solid. For lower temperatures, ethane or ethylene are suitable, particularly when evaporated under diminished pressures (subatmospheric). If desired, two or more refrigerants may be employed in different parts of the system, thus an ammonia system may be used to reduce the temperature in those chillers handling the heavier fractions. It is necessary to cool the lighter fractions to a much lower temperature to efiect the desired separation of solid hydrocarbons. By proper routing, and use of heat exchange, it is possible to carry out the process by applying direct refrigeration to the lighter fractions only, cooling the heavier fractions solely byheat exchange with the products obtained by separating the light fractions.

Referring again to the drawings, the refrigeration cycle may be described as follows: Liquid carbon dioxide in reservoir 24 is led by line 25 to coolingcoil 26 in chiller 21. Expansion of the liquid occurs at expansion valve 27 and the escaping gases are returned by line 28 to com: pressor 29'where they are compressed and cooled by cooler 30 and condensed in exchanger 16 pre viously described. The liquefied refrigerant then returns to the storage by line 31. The cycle is similar for the remaining chillers and need not be described in detail.

As previously mentioned, the refrigerant may be added directly to the gasoline fraction, preferably after .precooling both the gasoline fraction and the liquid refrigerant with suitable heat exchange. Operating in this way, it is necessary to control the pressure in order to control the refrigeration, thus by reducing the pressure on the mixture of liquid refrigerant and hydrocarbon any suitable temperature can be obtained down to the boiling temperature of the refrigerant at the lowest pressure available. Where a refrigerant liquid isemployed which is miscible with the gasoline hydrocarbons it may often be desirable to allow a portion of the refrigerant liquid to remain in the gasoline during the operation wherein the solid hydrocarbons are separated. Thus, when liquid ethane is employed, it is found that the settling rate of the solid hydrocarbons is increased by virtue of the low viscosity and low density of the liquid ethane. After the separation has been made the refrigerating effect of the remaining ethane can readily be realized by evaporation in suitable heat exchangers. that all the low temperature apparatus described in the accompanying drawings must be heavily insulated to reduce refrigeration losses to a minimum.

Fig. 2 illustrates an apparatus suitable for carrying out the process in the above manner. A gasoline fraction which may be a narrow boiling range fraction of straight-run or cracked gasoline is introduced by line 50 to mixer 51 where it is brought into contact with a stream of suitable refrigerating liquid, for example, liquid ethane, introduced by line 52. The mixture passes by line 53 and reducing valve 54 to refrigerating chamber 55 which is heavily insulated. The pressure in this chamber may be maintained at or near atmospheric pressure and as a result a large proportion of the refrigerant evaporates, the vapors being conducted away by line 56'. As a result of the evaporation the gasoline is cooled to a very low temperature and the undesirable paraflinic constituents are separated as a crystalline magma, which is led by line 57 and pump 58 to continuous filter 59 where the unsolidified portions are filtered off and discharged by line 60. The solidified portions from the filter pass by a screw conveyor into line 61 and pump 62 to chamber 63 which is warmed by heat from coil 64 sufficient to liquefy the solids and expel any remaining refrigerant. The vapors of the refrigerant are discharged by line 65 and the separated gasoline fraction by line 66.

The filtrate in line 60 is forced by pump 6'7 into chamber 68 where it is likewise heated by coil 69 and thereby freed from remaining refrigerant, the vapors of which are discharged by line 70. The gasoline fraction is withdrawn-by line 71 and forms the desired high octane value gasoline. The vapors from chambers 63 and 68 are led by line'72 to condenser 73 under sufficient pressure to cause liquefaction, liquid refrigerant'bee' ing collected in refrigerant storage tank 74; The refrigerant vapors from the chamber 55' and the filter 59 are'led by lines 56 and 75 to compressor 76 which raises the pressure sufficiently forcom densation in the condenser 73. As an example of some results obtained by It should be understood, of course,-

the use of this process a straight-run Mid-Conti carbons which solidified at this temperature were separated and the supernatant liquid was again chilled to minus 80 F. followed by a separation into a solid portion and a liquid portion. The liquid portion from the second separation was added to a gasoline having an octane number of 62, using the proportion of 25% of the heavy naphtha and of the 62 octane number gaso-v line. The resulting gasoline had an octane number of 48.

The solid hydrocarbons from the first separation were mixed with the same 62 octane number gasoline in the same proportion and gave a blend having an octane number of 46. The difference of two octane numbers corrected for the percentage of heavy naphtha employed, indicates a difference of 8 octane numbers between the two heavy naphtha fractions.

In another example a straight run heavy naphtha from a Michigan crude was fractionated to produce a heavy naphtha boiling between 320 and 450 F. This naphtha was chilled to minus F. and the solid hydrocarbons crystallizing at this temperature were filtered therefrom and constituted about one-third of the heavy naphtha by volume. When 25% of the separated solid hydrocarbons were added to 75% of a 64 octane number gasoline the resulting blend had an octane number of 44. When the liquid fraction was likewise blended with the same 64 octane number gasoline in the same proportion the resulting blend had an octane number of 48. The difference when corrected for percentage composition in the blend amounts to 16 octane numbers.

These results are by way of example only and it is obvious that more striking differences can be obtained by more accurate control. Thus experience shows that the narrower the boiling range of the fractions treated, the more effective is the separation of the undesirable knock-induc-' Although the process of this invention is particularly applicable to the separation of knock inducing constituents from gasoline and motor fuels, it is also applicable to the production of premium burning oils, lamp distillates, kerosene, etc. When applied to a kerosene having undesirable burning characteristics imparted by the presence of naphthenic hydrocarbons, the solidified fractions obtained by low temperature refrigeration are found to possess superior burning properties. The unsolidified fractions are suitable for tractor fuel and other purposes. For the separation of burning oils and kerosene it is unnecessary to refrigerate to temperatures as low as those required for gasoline separation.

This invention has been described by its application to certain typical problems but its scope is not intended to be limited by these applications except as set forth in the following claims:

I claim:

1. The process of separating undesirable knock inducing constituents from gasoline and kerosene motor fuels comprising refrigerating the fuel to a low temperature, permitting a portion of the hydrocarbon constituents to solidify and separating the solidified hydrocarbons from the unsolidified hydrocarbons.

2. The process of claim 1 wherein the hydrocarbon motor fuel is a gasoline of intermediate antiknock value having an octane equivalent between 50 and 70.

3. The process of claim 1 wherein the hydrocarbon motor fuel is a cracked gasoline.

4. The process of claim 1 wherein the hydroca bon motor fuel is a tractor fuel.

5. Theprocess of producing high knock rating gasoline from low knock rating gasoline comprising fractionally distilling said gasoline to produce ing hydrocarbons. Enhanced results can also be a plurality of narrow boiling fractions, subjecting obtained by further recrystallization.

Another method of carrying out the separation of knock inducing constituents from gasoline is to subject the gasoline to a refrigerating operation sufficiently severe to totally solidify the gasoline, subsequently allowing the temperature to rise gradually, whereupon the solidified gasoline is preferentially melted or sweated. By carefully controlling the temperature the knock inducing constituents may be allowed to remain behind in the solid condition. By diverting the drips at different stages of the sweating operation it is possible to obtain a variety of fractions, the first fractions possessing the highest antiknock characteristics.

As in the previously described separation by' fractional crystallization, it is highly desirable to carry out the sweating operation on a narrow boiling fraction of the gasoline rather than on the composite gasoline mixture. However, if the operation is conducted on the entire gasoline composite the fractions obtained during the sweating operation may be subsequently separated by distillation into high and low anti-knock fractions which may be suitably combined to give the desired high antiknock gasoline.

The sweating operation may suitably be carried out in a refrigerated chamber equipped with cooling coils to supply indirect refrigeration. After the gasoline hydrocarbons have been solidified the temperature of the refrigerant in the coils may be allowed to increase gradually by any suitable means, such as applying increased pressure. In this way it is possible to obtain uniform temperature control throughout the entire body of hydrocarbons.

fuel.

7. The process according to claim 5 wherein only the heavy naphtha fractions of the gasoline are subjected to further separation by refrigeration.

8. The process of producing a superior kerosene comprising subjecting a kerosene distillate to a refrigeration operation wherein a portion of the distillate is caused to solidify, separating the solidified portion from the unsolidified portion.

9. The process of separating from a light petroleum distillate such as gasoline and kerosene those components which are responsible for detonation in an internal combustion engine, comprising solidifying the distillate by extreme refrigeration, gradually raising the temperature of the solidified distillate whereby it is progressively liquefied, separately collecting the liquefied distillate in a plurality of fractions and rejecting the CERTIFICATE oi co'RREcTroN.

latent No. 1,951,780. March 20, 1934 VANDERVEER VOORHEES.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line 1221, claim 6, before "together" insert blended; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of May, A. I). 1934.

Bryan M. Battey (Seal) Acting Commissioner of Patents. 

